The overall objective of this proposed research is to establish the mechanism responsible for the regulation of leucine oxidation by mammalian cells. Studies will be conducted with isolated hepatocytes, perfused rat heart, ascites tumor cells, isolated liver mitochondria, isolated liver peroxisomes, various transaminases active with leucine, and the alpha-ketoisocaproate dehydrogenase complex isolated from liver tissue. The specific aims include: (a) to determine the role of peroxisomes and glyoxylate aminotransferase in the oxidation of leucine by the liver; (b) to determine whether dichloroacetate is converted to glyoxylate and oxalate by the liver; (c) to establish whether the alpha-ketoisocaproate dehydrogenase complex is 'interconvertible' by a phosphorylation-dephosphorylation mechanism; (d) to establish how dichloroacetate activates the oxidation of alpha-ketoisocaproate by the perfused rat heart; (e) to determine whether valine toxicity observed in patients with the nonketotic form of hyperglycinemia can be explained by the effects of either glycine or glyoxylate on the catabolism of valine; (f) to further investigate the effects of pyruvate, dichloroacetate, and glyoxylate on leucine catabolism by neoplastic tissue; and (g) to further investigate the regulation of leucine metabolism by the apparent adaptive changes in the activities of alpha-ketoisocaproate dehydrogenase and leu-tRNA synthetase which we have observed in the liver of the protein-starved rat. An important working hypothesis of the study is that peroxisomes and glyoxylate aminotransferase play an important role in the catabolism of leucine.